Method forming a one-piece articulating spacing device for a knee joint

ABSTRACT

The present invention provides molds and methods for producing articulating spacers that are custom-fit to the bone and can be used in two-stage revision knee arthroplasty and other orthopaedic surgery.

RELATED APPLICATION

This application claims priority and other benefits from U.S.Provisional Patent Application Ser. No. 61/178,974, filed May 17, 2009,entitled “Mold and method of forming an articulating spacing device fora joint”. Its entire content is specifically incorporated herein byreference.

STATEMENT OF GOVERNMENTAL SUPPORT

This invention was made with support of the U.S. Government representedby the Department of Veterans Affairs. The Government has certain rightsin this invention.

TECHNICAL FIELD OF THE INVENTION

The present invention relates to the field of implants for use inorthopedic surgery, in particular, for use in creating a temporaryarticulating spacer in two-stage reimplantation total knee arthroplasty.

BACKGROUND

The anatomy of the knee is primarily composed of two major bones, thetibia and the femur (see FIG. 1). These two bones meet to form a jointbetween the proximal tibia and the distal femur. A third member of thejoint is the patella, or the kneecap. The knee joint is cushioned byarticular cartilage that covers the ends of the tibia and femur, as wellas the underside of the patella. The lateral meniscus and medialmeniscus are pads of cartilage that further cushion the joint, acting asshock absorbers between the bones.

A healthy knee joint is able to withstand great forces that are exertedas the knee flexes and extends and supports the weight of the body.However, when the knee joint degenerates and becomes arthritic due to aninjury or infection of the joint or due to aging, it may becomenecessary to reconstruct or replace the knee joint. When a total kneereplacement (arthroplasty) is required, the natural knee joint isreplaced with a prosthetic knee joint. A certain percentage of patientswho undergo a total knee replacement surgery eventually contract aninfection in the knee joint at the surgical site necessitating furthersurgery for control of the infection.

Two stage reimplantation total knee arthroplasty has become anincreasingly common operation for the treatment of infected total kneearthroplasty. The treatment of infected total knee arthroplasty requiresthe removal of the old prosthesis (artificial joint) and placement of aspacing device to treat the infection before a new prosthesis isimplanted. The spacing device is needed, since it is important tomaintain the original space between the joints in order to prevent areduction in the articular space (see FIG. 2), retraction of thetissues, atrophy of the joints and loss of muscular elasticity as wellas tone. In addition, the spacing device contains antibiotics that elutefrom the spacer after implantation, locally delivering antibiotics tothe site of the infection. This is an essential part of the overalltreatment to eradicate the infection.

Non-articulating as well as articulating spacing devices are known inthe art for artificial knee, hip and shoulder joints. Traditionalnon-articulating, fixed spacing devices for the knee are applied as abone cement block that is mixed with antibiotics by the surgeon and isplaced between the tibia and the femur. Though these fixed spacingdevices have been shown to be effective in treating infections andmaintaining space for reimplantation of a second knee replacement afterthe infection has been eradicated, these spacers do not allow for kneemovement. As treatment for infection after knee replacement can takemany months, it is very inconvenient for the patient to not be able tomove his knee for such an extended period of time.

Prefabricated and preformed articulating spacing devices made of bonecement and other materials exist that allow the patient limited mobility(e.g. Interspace® knee spacer from Exactech, Gainesville, Fla.), but, aswith limited size options, do not provide an optimal fit to theparticular bony anatomy of each patient. In addition, preformedarticulating spacing devices do not give the surgeon the flexibility toselect the type and concentration of antibiotic in the spacer. Sincedifferent bacteria have different sensitivities to differentantibiotics, this is a significant disadvantage.

Other existing technologies (e.g. Stage One molds, Biomet Inc.) involvethe surgeon using two preformed molds to make articulating spacers. Withthese technologies, the surgeon can select the type and concentration ofantibiotic in the cement, but the molding process occurs outside of thepatient in two separate molds, one mold to create the femoral spacercomponent, and the other to create the tibial spacer component. Thesurgeon must then wait for the cement to harden, remove the spacer fromeach mold, and then either place these two molded articulating spacercomponents in the patient, and not achieve a custom fit with theirregular bone surface of the patient, or the surgeon must then mix asecond batch of cement to cement these spacers on the patients bone.Though this solution provides the surgeon with the capability ofselecting the type and concentration of antibiotic in the spacer, theonly way to achieve a custom fit with the irregular bone surface of eachpatient is to mix two batches of cement, one to make the moldedcomponents and the other to apply them to the existing irregular bonesurfaces of the patient, a process that takes considerable valuableoperating room time.

Another proposed solution to this problem involves placing sterile metaland plastic knee replacement components in the knee with cement that hasbeen mixed with antibiotics. This solution is controversial as itinvolves placing a large quantity of inert material (metal and plastic)that does not elute antibiotics into the infected site.

Reproducing the knee joint using custom-fit temporary spacing devicesthat have only antibiotic eluting material and that simulate the naturalshape of the tibial and femoral components of the knee joint would besuperior to the fixed spacing devices, since they provide an optimal fitto the particular bony anatomy of a patient, permit movement of the leg,and can still deliver antibiotics to aid in the treatment of infectionand maintaining space for future surgery. There is a clear need in theart for custom-fit articulating spacers that provide the surgeon withthe ability to deliver a specific antibiotic at a specificconcentration, that only require one round of mixing cement, and that donot require post-molding modification.

The present invention fully addresses this need.

SUMMARY

The present invention provides compositions and methods for forming andclinically utilizing articulating spacing devices. In a particularembodiment of the present invention, an articulating spacing device fortwo stage knee arthroplasty is described which uses molds that areshaped like a very thin femoral component of a total knee replacementand that are available in different sizes to fit the size of eachpatient.

Those having ordinary skill in the relevant art will appreciate theadvantages provided by the features of the present invention. Forexample, it is a feature of the present invention to providecustom-sized molds for the knee joint that are formed in situ duringsurgery which are practical, time-efficient and inexpensive tomanufacture, as well as adaptable to various bony anatomy. Aparticularly noteworthy and advantageous feature of the presentinvention which has not been a feature of other molds previouslydescribed for creating an articulating cement spacer is that one singlemold simultaneously molds the cement on both sides of the joint (thedistal femur and the proximal tibia), and does this in situ (in thepatient) requiring only one mixing of cement. Further objectives of thepresent invention are to provide a method of forming a temporary spacingimplant that simulates the biomechanics of the joint, for example thenatural knee joint, such that a patient may have mobility and range ofmotion in the knee joint during the time of implantation and before therevision surgery.

The above summary is not intended to include all features and aspects ofthe present invention nor does it imply that the invention must includeall features and aspects discussed in this summary.

INCORPORATION BY REFERENCE

All patent and non-patent publications mentioned in this specificationare herein incorporated by reference to the same extent as if eachindividual publication or patent application was specifically andindividually indicated to be incorporated by reference.

DRAWINGS

The accompanying drawings illustrate embodiments of the invention and,together with the description, serve to explain the invention. Thesedrawings are offered by way of illustration and not by way oflimitation; it is emphasized that the various features of the drawingsmay not be to-scale.

FIG. 1 shows a lateral view of a knee.

FIG. 2 shows a lateral diagram of a knee with destruction of the jointsurface and view of the articular space.

FIG. 3 demonstrates how, in accordance with an embodiment of the presentinvention, the material to be molded is placed on one side of the jointand within the concave side of the mold; in a particular embodiment ofthe present invention, the mold is made out of sheet metal and designedfor molding bone cement, which has been mixed with at least oneantibiotic. The material to be molded can be first placed on the tibiaand then into the concave of the mold or vice versa. Apart from sheetmetal, the mold can be made out of any other rigid material such asanother metal or hard plastics or an elastic material such as silicone.

FIG. 4 demonstrates, in accordance with an embodiment of the presentinvention, how the mold of FIG. 3 is pressed onto the other side of thejoint. The concave side of the mold forms one side of the newly formedjoint surface and the convex side of the mold simultaneously forms theother side of the joint surface.

FIG. 5 illustrates, in accordance with an embodiment of the presentinvention, how the material has conformed to the irregular bone surfaceon each side of the joint, and, with removal of the mold, the materialhas been formed into mating parts at the new joint surface such thatthey can articulate with one another.

FIG. 6 shows, in accordance with an embodiment of the present invention,a mold made out of stainless sheet metal where a lubricant such asmineral oil is applied to both its concave (PanelA) and convex sides(PanelB), to facilitate easy detachment from the cement to be molded.

FIG. 7 shows, in accordance with an embodiment of the present invention,a stainless sheet-metal mold whose concave side is being filled with amolding bone cement-antibiotic mixture.

FIG. 8 shows, in accordance with an embodiment of the present invention,a bone cement-filled sheet-metal mold that has been applied onto thedistal femur.

FIG. 9 shows, in accordance with an embodiment of the present invention,a bone cement-filled sheet-metal mold that has been applied onto thedistal femur, where, in addition, pliable cement has been applied to thetibia, while the knee has been maintained in an extended position. Thesheet-metal mold is acting to simultaneously mold the cement on both thefemoral and tibial sides of the joint.

FIG. 10 shows, in accordance with an embodiment of the presentinvention, an articulating spacing device created out of molding bonecement. The spacing device (‘spacer’) exhibits two mating surfaces thatallow for knee extension (PanelA) and knee flexion (Panel B).

FIG. 11 shows postoperative x-rays of a patient with an articulatingspacing device made out of bone cement, in accordance with an embodimentof the present invention. PanelA shows a frontal view and Panel B showsa lateral view.

FIG. 12 shows a typical example of range of motion two weeks followingimplantation of an articulating spacing device, in accordance with anembodiment of the present invention. Panel A illustrates an extendedposition, while Panel B illustrates a flexed position.

DEFINITIONS

The practice of the present invention may employ conventional techniquesin total knee and revision arthroplasty, which are within thecapabilities of a person of ordinary skill in the art to which thepresent invention belongs. Such techniques are fully explained in theliterature. For definitions, terms of art and standard methods known inthe art, see, for example, Scuderi and Tria “Knee Arthroplasty Handbook:Techniques in total knee and revision arthroplasty”, Springer 2006,which is in its entirety herein incorporated by reference.

Unless defined otherwise, all technical and scientific terms used hereinhave the same meaning as commonly understood by a person of ordinaryskill in the art to which the present invention belongs. The followingdefinitions are intended to also include their various grammaticalforms, where applicable.

The terms “spacing device” and “spacer” are used interchangeably.

The terms “temporary spacing device”, “temporary spacing implant”,“custom-fit spacing device”, “custom-fit spacing implant” are usedinterchangeably.

DETAILED DESCRIPTION

The present invention provides compositions and methods for forming andclinically utilizing articulating spacing devices; such methods arecarried out in the course of the surgery and, therefore, require minimaladditional time. In a particular embodiment of the present invention, anarticulating spacing device for two stage knee arthroplasty is describedwhich is formed using molds that are shaped like a thin femoralcomponent of a total knee replacement. The molds can be supplied in anarray of sizes to meet various individuals' needs and to accommodate allthe potential possibilities in anatomical differences of individuals;for example, the molds can be supplied in five different mold sizes(extra small, small, medium, large, extra large). More or less than fivemold sizes may be used by the present invention, dependent upon thedesired range of bones to be fitted by the molds.

In certain embodiments, the molds to form a temporary spacing implantare shaped like a femoral component of a total knee replacement. Inother embodiments, the molds to form a temporary spacing implant includea convex and a concave side, where the concave side of the mold formsone side of the newly formed joint surface and the convex side of themold forms the other side of the joint surface.

In certain embodiments, the molds to form a temporary spacing implantare made out of sheet-metal. In other embodiments, the molds to form atemporary spacing implant are made out of an alternative metal, metalalloy or a rigid plastic or out of an elastic material such as silicone.

In certain embodiments, the molds to form a temporary spacing implantare used to create an implant out of bone cement that can be mixed witha standard antibiotic in a typical concentration, as known in the art oforthopedic surgery. In other embodiments, the molds to form a temporaryspacing implant are used to create an implant out of a biocompatiblematerial other than bone cement; such biocompatible material may bepresently known or may become known in the future in the art to formsuch implants and can be a synthetic material or a material originatingfrom tissue engineered cells. Therefore, it is contemplated that amyriad of other materials that are also biocompatibly suitable forsurgical use may be utilized as the implant material without departingfrom the scope of the present invention.

Advantageously, embodiments of the spacing devices of the presentinvention allow for custom molding to fit the particular bony anatomy ofeach individual patient and allow mobility and flexion of the concernedjoint.

Arthroplasty

Arthroplasty is a surgical procedure to reconstruct and/or realign ajoint that has become dysfunctional due to injury or aging with theobjectives to minimize joint pain, to stabilize the joint and to restorerange of motion as best as possible. Osteoarthritis, a degenerativejoint disease, is the most common condition causing joint dysfunctionand even joint destruction followed by severe pain and impaired jointmovement due to joint stiffness.

Each joint has, in a healthy condition, a specific range of motion whichis expressed in degrees and which indicates the direction and distance ajoint can maximally move.

Joint resection and interposition to create a new articulating surfaceis known as arthroplasty surgery and is common in the hip, knee,shoulder, ankle, elbow, and finger joint. Isolated joint resection(resection arthroplasty) results in an increased space between thearticulating bones, usually improving the range of motion and decreasingpain. Resection arthroplasty, however, does not recreate a stablearticulating joint, resulting in weakness and instability.Reconstructing the joint surface with interposed material such as aprosthesis can achieve pain relief, improve range of motion, and providea stable and strong joint. Such a prosthesis can be synthetic and bemade of plastic, metal, ceramic or can be formed from body tissue suchas skin, muscle or fascia.

In recent years, total joint replacement or total joint arthroplastywith artificial joints (prostheses) has become a feasible and oftenpreferred choice of treatment for advanced arthritis of the hip andknee. Since currently available artificial joints (in particular,artificial knee and hip joints) may have a limited life span, andrepeated joint replacement is not always possible, prosthetic jointreplacement must be used with caution in the younger and more activepatient.

Surgical Intervention at the Knee: Total Knee Arthroplasty

Several procedures are available to correct joint dysfunction rangingfrom corrective surgeries to total knee replacement. Total kneearthroplasty has become a reliable and reproducible procedure for painrelief and restoration of function in knees with advanced arthritis ofthe knee (Hofmann et al., 2005). Unfortunately, approximately 1% to 2%of total knee arthroplasties will get infected. Debridement andretention of knee replacement components can be successful in treatingacute, early infections, but has not been very successful in treatingdeep, chronic infections. In the latter case, the infected implants mustbe removed. Reimplantation can be carried out in one (single) stage(single-stage exchange arthroplasty) or in two stages (Whiteside L A,1994; Wilde & Ruth, 1988). Two-stage reimplantation for infected kneereplacement has been demonstrated to be consistently more effective thansingle-stage reimplantation and is the current standard technique.

The standard treatment for two-stage reimplantation (revision) totalknee arthroplasty is to remove the implanted components, place some sortof an antibiotic impregnated cement spacer to deliver antibioticslocally and maintain space for eventual knee replacement reimplantation,and then treat with antibiotics for a minimum of six weeks to eradicatethe infection. Once the infection is proven to be eradicated, a newtotal knee arthroplasty can be implanted.

Two-stage reimplantation (revision) total knee arthroplasty includes thefollowing procedures. As a first step, the previously implantedprosthesis is surgically removed and the site debrided and thoroughlycleansed. Before a new, permanent prosthesis can be placed in the oldsurgical site, the infection has to be cleared, which usually can takefrom six weeks to four months. Therefore, it is common for surgeons toreplace the old prosthetic knee with a temporary implant during the timewhen the infection is cleared up and before the new prosthesis issurgically implanted. The temporary implant is a spacing device, whichis typically impregnated with an antibiotic as part of the therapy torid the surgical site of the infection and which can be made of variousmaterials that do or do not contain bone cement (Whiteside La., 1994).

Utility of the Present Invention

Reproducing the knee joint using temporary spacing implants thatsimulate the natural tibial and femoral components of the knee joint isdesirable because it permits the patient to move his/her leg through arange of motion. Before a new, permanent prosthesis can be placed in theold surgical site, any infection has to be eradicated be treating withantibiotics, which can take from six weeks to four months or longer(‘treatment period’). A patient's comfort and emotional well-beingduring this ‘treatment period’ is clearly affected by the patient'srange of motion. Accordingly, any increase in the range of motion, byallowing the patient to bend his/her knee for sitting in a chair or forriding in a car, will directly increase the patient's comfort andemotional well-being during the ‘treatment period’.

Complete immobilization of the knee in an extended position for theentire course of the treatment period can make revision surgery moredifficult due to the immobility of the tissues. Prefabricated spacingdevices made of cement and other biocompatible materials exist (e.g.Interspace® knee spacer from Exactech, Gainesville, Fla.), but—incontrast to the herein described custom-fit spacers as certainembodiments of the present invention—do not provide an optimal fit tothe particular bony anatomy of each patient. A poorly fitting cementspacer can move excessively in relation to the bone it is applied to,and this movement can be painful. Additionally, the prefabricatedspacers are supplied with a certain antibiotic at a certainconcentration. This may not be optimum for treatment of the infection.

The mold and technique of the present invention allow for customfabrication of the cement spacer with type and concentration ofantibiotics specific for the infection being treated, and for a customfit to the existing bone surfaces. This minimizes any relative movementagainst the bone and, therefore, minimizes pain, while allowing forrange of motion of the joint. The time required to make the spacingdevice with the mold and technique of this invention is minimized asonly one cement mixing is needed.

In contrast to spacing devices that are in their entirety manually madeby the surgeon carrying out the implantation of that device at the timeof the surgical operation, the present methodology enables the surgeonto provide the proper, anatomically correct spacing for optimal healingand range of motion. Furthermore, unlike fully manual procedures, thepresent methodology requires minimal additional time by the surgeon,since it is made with the assistance of a mold, is molded in the wound,molds the femoral and tibial components of the spacer at the same time,requires only one mixing of cement, and does not require anymodification of the spacer once the cement has hardened.

While an articulating spacing device for use in two-stage total kneearthroplasty is a preferred embodiment of the present invention,embodiments of the present invention are also envisioned and suitablefor use in shoulder joint, elbow joint, ankle joint, wrist joint and hipjoint reconstruction.

With respect to joint movement and degrees of movement, the knee isapproximately a uniaxial joint with flexion and extension occurringaround a single axis and movement in one plane; it enables extension(straightening) and flexion (bending) of the lower leg. The ankle, elbowand finger joints are similar uniaxial joints and a spacer mold forthese joints would be similar in design. The shoulder, wrist and hipjoints are multiaxial joints with three degrees of freedom and movementin three planes. A spacer mold can be fashioned for these joints, but itwould have a hemispherical shape rather than a cylindrical shape inorder to allow this multiaxial movement.

In conclusion, articulating spacing devices of the present inventionutilize elements in several sizes (molds made out of a rigid or elasticmaterial). The surgeon selects the proper sized mold for the patient anduses this single mold to produce both members of the articulating spacerby simultaneously molding both sides of the joint while the cementhardens in situ. In case of total knee arthroplasty, articulatingspacing devices of the present invention simulate the natural shape ofthe femoral and tibial components of the knee joint.

All members are made out of biocompatible material.

Exemplary Procedure for Creating an Articulating Spacing Device for theKnee

In practice, a mold, as exemplified in FIG. 6, Panels A and B, may beused in situ by the surgeon in the following manner. First, bone cementor another biocompatible material known in the art for the fabricationof temporary implants, is mixed together with an antibiotic (or asuitable mixture of antibiotics, meaning a mixture of antibiotics whichdo not adversely interact, are effective against the bacterial infectionbeing treated, and, in the total dosage, do not exceed the safe,therapeutic window) and pressed into the cavity of the mold (see FIG.7). Cement is then applied within the concave surface of the mold andthe mold is then, in accordance with an embodiment of the presentinvention, applied to the distal end of the femur. Additionally,directly before or after application of the mold to the distal end ofthe femur, more still pliable bone cement (or other biocompatiblematerial known in the art) is applied to the tibial surface. Both thefemoral and tibial cement then harden simultaneously, with the moldacting to form both sides of the articulation simultaneously while theknee is held in proper alignment and in an extended position. Once thecement (or other biocompatible material known in the art) has completelycured and hardened, the surgeon may remove the mold by pulling the moldoff of the femur. The removal process acts as the last step in formingboth the femoral and tibial components of the temporary spacing implant.It is noted that the removal of the mold may be accomplished by avariety of methods utilizing a variety of devices, each of which areintended to fall within the scope of the present invention.

In accordance with the features described above, a useful method forforming an articulating spacing device for a patient's knee jointincludes the steps of:

-   -   (a) providing a rigid or elastic mold made out of metal such as        sheet-metal, metal alloy, metalloid such as silicon, ceramics,        natural or synthetic polymers, said mold being available in many        different sizes to accommodate all the potential possibilities        in anatomical differences of patients and said mold shaped        preferably like a thin femoral component of a total knee        replacement;    -   (b) providing a biocompatible material such as bone cement,        mixed with a standard amount of antibiotics as commonly known        and used in the art, and substantially filling the cavity of the        mold with said biocompatible material to a desired thickness;    -   (c) positioning the mold on the distal end of the femur;    -   (d) adding additional biocompatible material to the tibial        surface;    -   (e) extending the knee and holding the leg in proper alignment,        allowing the mold to form both the tibial and femoral surfaces        as the molding mixture totally hardens;    -   (f) removing the mold from the femur.    -   Steps (c) and (d) can be reversed, yielding an identical        outcome.        Materials Suitable for Rigid Molds

The molds of the present invention can be provided in a rigid form andbe made out of a thin sheet of metal such as stainless steel, platinum,titanium, iridium, an metal alloy such as ferroalloys, alloys oftitanium, iridium, platinum or aluminum, a metalloid such as silicon, anon-metal such as ceramic or synthetic polymeric materials such as hardplastic.

Materials Suitable for Elastic Molds

The molds of the present invention can be provided in an elastic formand be made out of a natural elastomer such as rubber or a syntheticelastomer such as ethylene propylene polymers.

Biocompatible Materials (Including Bone Cement)

Materials for implantation must be biocompatible, i.e., it must notelicit an immune response, once implanted into a patient. Optionally, abiocompatible material is able to integrate with the tissue into whichit is implanted.

Biocompatible materials that are considered in the context ofembodiments of the present inventions include, but are not limited tothe different kinds of currently commercially available polymethylmethacrylate-based bone cements. Polymethyl methylacrylate (PMMA) is asynthetic polymer of methyl methacrylate and is produced bypolymerization of powdered pre-polymerized polymethyl methacrylate andliquid monomethy methacrylate monomers.

Antibiotics Suitable for Release from Biocompatible Materials Used in anArticulating Spacing Device

Antibiotic-loaded bone cement is an effective and proven method forlocally delivering antibiotics. Low-dose antibiotic-loaded bone cements(<0.9 g of powdered antibiotic per 10 grams of bone cement) were firstapproved by the FDA in 2003 for second-stage reimplantation afterinfected arthroplasties. Nowadays, commonly used concentrations ofantibiotic-loaded bone cements range from 0.9-2 g (or higher) ofpowdered or liquid antibiotic per 10 g of bone cement, depending on theintended purpose, which might be prophylactic to protect against aninfection or aggressive in case of the treatment of a high-risk jointthat is infected with a possibly drug-resistant organism.

Antibiotics that are commonly used in arthroplasty procedures include,but are not limited to, aminoglycoside antibiotics such as tobramycinsulfate or gentamicin sulfate (a typical concentration is 0.9 g ofpowdered or liquid tobramycin base or gentamicin base preparation per 10grams of bone cement) or glycopeptide antibiotics such as vancomycin (atypical concentration is 3 g of powdered or liquid vancomycin per 40grams of bone cement). The antibiotic cement mixture can be producedmanually by handmixing the appropriate amount of powdered antibioticwith the appropriate amount of bone cement or can be a premixed,commercially available formulation. Examples of commercially availableantibiotic-loaded bone cements include Simplex™ P with tobramycinsulfate, Palacos® R with gentamicin, SmartSet GMV with gentamicin orDePuy CMW bone cement mixed with vancomycin or gentamicin.

Complete Healing Parameters in Two-Stage Arthroplasty

Successful two stage reimplantation total joint arthroplasty involvesremoval of the original infected joint replacement and cement, thoroughdebridement of surrounding tissues, and placement of anantibiotic-eluting cement spacer. Antibiotics are also deliveredintravenously for an extended period of time, usually on the order ofsix weeks. Following this period of antibiotic administration, thepatient is typically taken off of antibiotics and monitored to ensurethat the infection has been eradicated, as indicated by standardlaboratory values including, but not limited to peripheral white bloodcell count, erythrocyte sedimentation rate, and C-reactive protein.Abnormally high levels of peripheral white blood cells or abnormallyhigh levels of C-reactive protein indicate an inflammation andlikely(continued) infection. An abnormally high erythrocytesedimentation rate is another indicator of inflammation and likely(continued) infection.

The joint itself can also be aspirated for cell count and culture torule out persistent infection. Once infection has been determined to beeradicated, a second operation is performed to remove the existingcement spacer and then reimplant a new total joint arthroplastyprosthesis.

Although any methods and materials similar or equivalent to thosedescribed herein can also be used in the practice or testing of thepresent invention, representative illustrative methods and materials areherein described. As will be apparent to those of skill in the art uponreading this disclosure, each of the individual embodiments describedand illustrated herein has discrete components and features which may bereadily separated from or combined with the features of any of the otherseveral embodiments without departing from the scope or spirit of thepresent invention. Any recited method can be carried out in the order ofevents recited or in any other order which is logically possible. In thefollowing, experimental procedures and examples will be described toillustrate parts of the invention.

Experimental Procedures

The following methods and materials were used in the examples that aredescribed below.

Materials

Implants consisted of DePuy CMW bone cement mixed with vancomycin (3.0grams per 40 gram package of bone cement).

Surgical Preparation

The patient was brought to the operating room and anesthesized. Theoperative leg was prepped and draped in the usual sterile fashion. Theinfected knee was exposed per the surgeon's preferred method and theinfected knee replacement components were removed. The knee wasthoroughly debrided of retained cement (and/or any other biocompatiblematerial used for the components) and infected tissue and the knee thenirrigated copiously. At this point, the surgeon was getting ready tocarry out the procedure for creating a custom-fit spacing device (seeexamples for more detail).

Clinical Evaluation

Postoperatively, a sterile dressing was applied and a drain was placedto suction. X-rays were obtained in the recovery room. The drain wasremoved at approximately 3 days postoperatively. Depending on thequality of the soft tissues and the type of surgical exposure employedat the time of surgery, range of motion was started on the firstpostoperative day with physical therapy. Weight bearing was restrictedto 50% of body weight. The patient was prepared for outpatient venousadministration of antibiotics, and the patient was discharged whenready. At two weeks post surgery, the patient returned for clinicalevaluation and wound check. Sutures or staples were removed from theskin and range of motion of the knee was checked. The patient wasencouraged to achieve and maintain as much motion as tolerable.Subsequent office visits were directed towards ensuring good woundhealing and following the progress of the treatment for infection. Fullweight bearing was allowed once the wound had fully healed.Reimplantation of the total knee arthroplasty was done when infectionhad been eradicated and soft tissues were amenable to surgery. This cantake from 6 weeks to 4 months or more.

EXAMPLES

The following examples are put forth so as to provide those of ordinaryskill in the art with a complete disclosure and description of how tomake and use the present invention; they are not intended to limit thescope of what the inventors regard as their invention. Unless indicatedotherwise, part are parts by weight, molecular weight is averagemolecular weight, temperature is in degrees Centigrade, and pressure isat or near atmospheric.

Example 1 General Working Protocol for Creating an Articulating SpacingDevice

General Working Protocol

1. Provide a mold that is sized in accordance to the bony anatomy of theindividual in need of arthoplasty. The mold can be made out of (i) arigid material such as a metal, e.g. stainless steel sheet metal, orhard plastic or (ii) an elastic material such as silicone. The moldmight be pretreated to facilitate easy detachment of the fillingmaterial from the mold or the mold can be manufactured from a rigid orelastic material that inherently facilitates easy detachment of thefilling material from the mold. 2. Mix the bone cement or otherbiocompatible material with antibiotics to obtain a standard antibioticconcentration (‘molding mixture’) 3. Before the molding mixture hardens,take half of the molding mixture and coat the concave side of the moldwith it (FIG. 3). 4. Flex the knee and press the mold filled withmolding mixture onto the end of the distal femur. 5. Take the remainingmolding mixture and place it on the tibial surface (FIG. 3). Thematerial to be molded can be first placed on the tibia and then into theconcave of the mold and onto the end of the distal femur or vice versa.6. Extend the knee, holding the leg in proper alignment while themolding mixture totally hardens (FIG. 4). The mold acts on both thetibial and femoral surfaces, and creates conforming surfaces compatiblewith motion of the joint. 7. Once the molding mixture has hardened, flexthe knee again and remove the mold. The material has conformed to theirregular bone surface on each side of the joint, thus achieving acustom fit, and the material has been formed into mating parts at thenew joint surface that can articulate with one another (FIG. 5). 8. Nowone has an articulating spacing device that is custom made for theresected bone surface(s).

Example 2 Process for Creating an Articulating Spacing Device Using aSheet-Metal Mold and Bone Cement-Antibiotics Mixture

Following the surgical preparation (see above under materials), theorthopaedic surgeon creates a bone cement-antibiotics mixture (‘cement’)by mixing bone cement with antibiotics such as tobramycin (3.6 grams per40 gram package of bone cement) or vancomycin (3.0 grams per 40 grampackage of bone cement).

Both sides of the sheet-metal mold are coated with mineral oil (FIGS. 6Aand 6B) to facilitate later on easy detachment of the cement from themold. The knee is fully flexed. When the cement is in a doughy state,the cement is applied to the concave side of the mold (FIG. 7). The moldis then gently pressed onto the distal femur (FIG. 8) and excess cementfrom around the mold is removed. Care is directed towards minimizing theamount of excess cement in the mold and the pressurization of cementinto the bone of the femur to allow for ease of later extraction. Careis also directed towards maintaining the proper level of the joint line.Additional cement, which is still doughy, is then applied to the tibia.The knee is then extended and held in the desired full extension with 6degrees of valgus (FIG. 9). The convex side of the mold forms the cementon the tibia into a shape that mates with the femoral side of the mold.The cement on both sides of the joint is then allowed to harden, whilethe leg is held in the proper position. When the cement is hard, theknee is flexed again and the mold is easily removed. One then has anarticulating cement spacing device for the knee with two mating surfacesthat allow for knee flexion and extension (FIGS. 10A and 10B). The woundis then closed over the articulating cement spacer. Only antibioticcement is left in the knee. There is no retained metal or polyethylene.Depending on the quality of the tissue overlying the knee and the typeof exposure performed, the patient may be allowed to begin range ofmotion exercises of the knee right after surgery. Postoperative x-raysare shown of a patient who received a spacing device, as described (FIG.11A frontal view and 11B lateral view). An example of range of motion atthe two week time point when the patient returned for suture removal isshown (FIG. 12A extended position and 12B flexed position).

Although the foregoing invention and its embodiments have been describedin some detail by way of illustration and example for purposes ofclarity of understanding, it is readily apparent to those of ordinaryskill in the art in light of the teachings of this invention thatcertain changes and modifications may be made thereto without departingfrom the spirit or scope of the appended claims. Accordingly, thepreceding merely illustrates the principles of the invention. It will beappreciated that those skilled in the art will be able to devise variousarrangements which, although not explicitly described or shown herein,embody the principles of the invention and are included within itsspirit and scope.

REFERENCES

-   Hofmann A A, Goldberg T, Tanner A M and Kurtin S M (2005). Treatment    of infected total knee arthroplasty using an articulating spacer.-   Clinical Orthopaedics & Related Research 430, pp. 125-131.-   Whiteside L A (1994). Treatment of infected total knee arthroplasty.-   Clinical Orthopaedics & Related Research 299, pp. 169-172.-   Wilde A H & Ruth J T (1988). Two-Stage Reimplantation in Infected    Total Knee Arthroplasty.-   Clinical Orthopaedics & Related Research 236, pp. 23-35.

1. A method of forming one-piece articulating spacing device for apatient's knee joint, the method comprising the steps of (1) providing arigid one-piece mold, said mold comprising: a main body portioncomprising a concave and a convex surface, wherein said body portion isshaped to allow controlled movement of said joint; a cavity defined bysaid concave and convex surfaces for receiving biocompatible material;wherein said mold is configured for being located, in situ, between thepatient's distal femoral bone and proximal tibial bone; wherein saidmold is dimensioned for custom forming said biocompatible material tooptimally fit to said patient's femoral and tibial bones; and whereinsaid mold is configured to form in situ an articulating surfacesimultaneously for articulation of the femoral surface with thecorresponding tibial surface. (2) placing a suitable amount of pliablebiocompatible material within said cavity; (3) contacting said patient'sfemoral bone with said biocompatible material within the concave surfaceof said mold; (4) with the mold on the femoral bone still in place,adding pliable biocompatible material to said patient's tibial bone insuch way that the resulting shape mates with the convex surface of saidmold; (5) letting said biocompatible material within said cavity of saidmold and on said tibial bone harden; (6) removing said mold.
 2. Themethod of claim 1, wherein said biocompatible material is mixed with atleast one antibiotic suitable for release from said biocompatiblematerial.
 3. The method of claim 1, wherein said articulating spacingdevice is a permanent spacing device for the knee.
 4. The method ofclaim 1, wherein said articulating spacing device is a temporary spacingdevice for the knee.